Historically, delimbing felled or harvested trees was performed manually using axes, hand saws and powered chain saws. This method of delimbing works well on large trees with sporadic branches because the weight of a felled tree trunk will snap many of the branches off the trunk leaving a minimal amount of delimbing to be performed. When smaller trees with many branches are felled, the trunk weight is often insufficient to cause the branches to snap off. Consequently, the hand delimbing process was dangerous and unpredictable, as well as time consuming.
As a result, delimbers have been developed which strip the branches off a whole tree at the harvesting site, thereby eliminating the need for manual delimbing and drastically reducing the time necessary for delimbing. The need for a delimbing machine has grown over the years as modern forestry practice has relied on clear cutting and forest thinning through the removal of smaller trees.
A popular type of delimber is the pull through delimber. The majority of pull through delimbers allow for a tree to be placed in the delimbing device with delimbing blades surrounding and parallel to the tree trunk. The tree is then pulled through the device with the blades cutting the branches as it traverses the assembly. The majority of these types of machines contain hydraulics or electronics causing them to be very expensive to purchase and operate. As a result of the high purchase and operating costs, many logging operations cannot afford to purchase such delimbers. Another disadvantage of these types of delimbers is that they only delimb one tree at a time. Additionally, most of these delimbing assemblies are very complicated with many moveable parts that are susceptible to damage and breakdown.
Another type of delimbing device is the mechanical pull through type. U.S. Pat. No. 5,406,997, to Davison, describes a mechanical pull through delimbing device that does not use any electronic or hydraulic components. Instead, the Davison device uses the weight of a tree to actuate the delimbing blades. In Davison, a tree is placed onto the assembly so that the weight of the tree rests on a lever causing a set of delimbing blades to close about the trunk. The trunk is then pulled through the delimbing assembly causing the branches to be stripped off the trunk. The Davison device eliminates the use of hydraulics and electronics; however, the assembly uses many moving parts that are susceptible to breakdown and jamming. Furthermore, the Davison delimber only allows for one tree to be placed into the assembly at a time resulting in a slow and tedious process in delimbing trees in a logging operation. An additional drawback associated with the Davison device is that it relies on the weight of the tree to close the blades. This method of operation is troublesome for small trees whose weight is insufficient to properly close the blades around the trunk. Davison also uses a spring to exert an opposite force on the support lever that is susceptible to stretching and breaking.